Terminology - Bosch DOMESTIC HOT WATER HEAT PUMP Technical Manual

During the process of repairs and manometer connections to the pressure gauges, check the eventual existence of
micro-leakages with an adequate equipment in order to avoid the lost of refrigerant gas to the atmosphere and
consequent malfunction in the appliance operation after your visit.
Pict.63 – Example of an electronic leakage detector from Testo

7.6 Terminology

Overheating of the refrigerant gas
In the fundamental process, the gas entering the compressor is assumed to be dry and saturated. In the reality the
gas is overheated. The overheating is the difference between the temperatures at the outlet of the evaporator.
It is a practical necessity to allow the refrigerant vapor to become superheated to prevent the carry-over of liquid
refrigerant into the compressor, where it may cause severe damage due to its incompressibility. It may also
contaminate the lubricants. The level of superheating should be kept to a minimum to minimize both the work to be
done by the compressor and the necessary heat transfer surface in the evaporator.
Sub-cooling of the refrigerant gas
In the fundamental process, the liquid leaving the condenser was just on the saturation line for liquids. The
pressure drop in pipes, filters, etc, before the expansion valve may cause problems and a small part of the liquid
can enter in vaporization. In order to avoid this, the condensed liquid is therefore sub-cooled to a temperature
below that of the saturation temperature corresponding to the condenser pressure, for two reasons:
The cooling capacity of the process is increased and the risk of gas bubbles in the fed to the expansion valve is
avoided (gas bubbles in the inlet flow to the expansion valve disrupt the regulation mechanism). The sub-cooling is
the difference between the temperatures at the end of the condenser.
6720649497 SM HP270-1 2012/09 en
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